Problems with Resins Traditionally Used
Plastics such as polyethylene terephthalate (PET) resin, polyester resin, vinyl chloride resin and polyolefin resin have been used as moldings for many applications, such as containers for foods, bottles for drinks, containers for cosmetics and flowerpots.
These plastics are mostly disposed of after use. Although these plastic wastes have been disposed of by incineration or landfill, disposal of such wastes by incineration has caused problems of: durability of incinerators that are exposed to high combustion temperatures due to high combustion energy generated by the plastic wastes being incinerated; disposal costs resulting from the installation of incinerators resistant to high temperatures; and air pollution caused by the generation of hazardous incineration gases such as carbon monoxide, sulfur compounds, chlorine gas and dioxin. As to disposal by landfill, it does not allow the plastic wastes to be decomposed, but to remain almost indefinitely and accumulate as wastes on waste disposal sites. This has given rise to a serious social problem with wastes. Moreover, since the plastic wastes exist in the ground in the as-disposed of form, they might produce a problem of unstable ground of landfills and affect the natural environment and various living organisms of the landfills and their vicinities.
As one solution to these problems, biodegradable resins have lately attracted considerable attention. The term “biodegradable resins” here means resins that have almost the same physical properties as those of general-purpose plastics when being used as materials, but, once disposed of, are promptly degraded by microorganisms in the natural environment, such as on the ground, in the soil, in compost, in activated sludge and in water. Biodegradable resins are degraded minutely and some of them are degraded to carbon dioxide and water.
As biodegradable resins that satisfy the above described requirements, not only specific polyester biodegradable resins, but also blended resin compositions, such as starch-ethylene-vinyl alcohol copolymer resins, ethylene-vinyl alcohol copolymer resins-aliphatic polyester resins and aliphatic polyester resins-polyolefin resins, have been known. And these resins or resin compositions have been shaped into various forms such as bottles and used for practical applications. However, excellent resin compositions have not been proposed yet that offer a good balance of moldability required in the production of containers, along with various physical properties required for the containers and biodegradability required after the containers are disposed of. For example, resin compositions have not been proposed yet such that have both biodegradability and heat resistance after molding.
<Polyhydroxyalkanoate (PHA)>
In recent years, there has been proposed, as a solution to environmental pollution caused by the wastes of plastic moldings etc., the use of biodegradable resins synthesized by microorganisms as molding materials. As biodegradable resins originated from microorganisms, have been known, for example, polyhydroxyalkanoates (hereinafter sometimes referred to as PHAs), such as copolymers of poly-3-hydroxy-n-butyric acid (hereinafter sometimes referred to as PHB) or 3-hydroxy-n-butyric acid (hereinafter sometimes referred to as 3HB) with 3-hydroxy-n-valeric acid (hereinafter sometimes referred to as 3HV) (hereinafter sometimes referred to as PHB/Vs), polysaccharides such as bacterial cellulose and pullulan, and polyamino acids such as poly-γ-glutamic acid and polylysine. Particularly PHAs are melt-fabricable and can be used for various products, like conventional plastics. In addition, they are excellent in biocompatibility; therefore, their applications to flexible members for medical use are also being expected.
Many types of microorganism have been heretofore reported to produce PHA and accumulate PHA in the cell31. It is known that such PHA may have various compositions and structures depending on the type of microorganism to be used for the production of the PHA, the culture medium composition and the culture conditions, and hitherto studies have been conducted mainly on control of the composition and structure of PHA to be produced in terms of improvements of physical properties of PHA.
Especially, biosynthesis of PHA obtained by polymerization of a monomer units with a relatively simple structure such as 3HB, 3HV, 3-hydroxyhexanoic acid (hereinafter referred to as 3HHx) and 4-hydroxy-n-butyric acid (hereinafter referred to as 4HB) have been studied, and production using various microorganisms has been reported1-7.
However, such straight-chain aliphatic polyesters as copolymers of 3HB or/and 3HV etc. tend to undergo thermal degradation because of close melting point and thermal degradation temperature. As a result, their extrusion workability is poor. Further, the straight-chain aliphatic polyesters are brittle due to their high crystallinity, and their extensibility tends to be low and mechanical properties tend to deteriorate. Thus, the straight-chain aliphatic polyesters alone are not preferable as materials for moldings.
In recent years, investigations have been made on a polyhydroxyalkanoate composed of medium-chain-length 3-hydroxyalkanoic acid units of about 4 to 12 carbon atoms (hereinafter sometimes referred to as mcl-PHA for short) vigourously.
It has been confirmed production of mcl-PHA using acyclic aliphatic hydrocarbons, octanoic acid, hexanoic acid, sodium gluconate etc. as a carbon source8,32,33. However, these mcl-PHAs have low melting points, and when the temperature is above 50° C., they become sticky and soft seriously. Thus, these mcl-PHAs alone are low in serviceability as materials for moldings.
The above described PHAs are all PHAs that are synthesized vai β-oxidation of hydrocarbons or via synthesis of fatty acid from saccharides in microorganisms and consist of monomer units having an alkyl group alone on their side chains (hereinafter referred to as usual-PHAs) or those similar to them (for example, PHA having an alkenyl group on side chains of which double bond is in the portion other than the end). However, if considering a wide range of application as a plastic, the above described PHAs are not satisfactory in terms of physical properties, at present.
For further expanding the range of, for Example, application of PHA, it is important to conduct a wide range of studies on the improvement of properties, and for this purpose, development and search of PHA including monomer units of a variety of structures is prerequisite. On the other hand, PHA with a substituent group introduced in the side chain (“unusual PHA”) can be expected to be developed as a “functional polymer” with very useful functions and properties originating from the introduced substituent group by selecting the introduced substituent group according to desired characteristics and the like. That is, it is also an important challenge to conduct of development and search of excellent PHA enabling such functionality and biodegradability to be compatible with each other. Examples of substituent groups include groups containing aromatic rings (phenyl group, phenoxy group, etc.), ester groups, unsaturated groups having a double bond on the terminal (alkenyl groups, alkadienyl groups, in particular, allyl groups), cyano groups, halogenated hydrocarbons and epoxide. For example, there are reports on production of: PHA containing a phenyl group or its partially substituted group such as PHA containing 3-hydroxy-5-phenylvaleric acid as a unit using 5-phenylvaleric acid as a substrate34-36, PHA containing 3-hydroxy-5-(4′-tolyl)valeric acid as a unit using 5-(4′-tolyl) valeric acid as a substrate37, and PHA containing 3-hydroxy-5-(2′,4′-dinitrophenyl)valeric acid and 3-hydroxy-5-(4′-nitrophenyl)valeric acid as a unit using 5-(2′,4′-dinitrophenyl)valeric acid as a substrate38; PHA containing a phenoxy group or its partially substituted group such as PHA containing 3-hydroxy-5-phenoxyvaleric acid and 3-hydroxy-9-phenoxynonanoic acid using 11-pheoxyundecanoic acid as a substrate39, PHA containing a 3-hydroxy-4-phenoxybutyric acid unit and a 3-hydroxy-6-phenoxyhexanoic acid unit from 6-phenoxyhexanoic acid, PHA containing a 3-hydroxy-4-phenoxybutyric acid unit, a 3-hydroxy-6-phenoxyhexanoic acid unit, and a 3-hydroxy-8-phenoxyoctanoic acid unit from 8-phenoxyoctanoic acid, and PHA containing a 3-hydroxy-5-phenoxyvaleric acid unit and a 3-hydroxy-7-phenoxyheptanoic acid unit from 11-phenoxyundecanoic acid40. There is also a report9 on a homopolymer consisting of 3-hydroxy-5-(monofluorophenoxy)pentanoate (3H5(MFP)P) units or 3-hydroxy-5-(difluorophenoxy)pentanoate (3H5(DFP)P) units, and a copolymer containing at least (3H5(MFP)P) units or (3H5(DFP)P) units, of which advantage is to provide stereoregularity and water repellency while maintaining a high melting point and good processability.
Further, studies are conducted on cyano-substituents and nitro-substituents in addition to the fluorine-substituent described above. For example, PHA containing 3-hydroxy-p-cyanophenoxyhexanoic acid or 3-hydroxy-p-nitrophenoxyhexanoic acid as a monomer unit is produced using octanoic acid and p-cyanophenoxyhexanoic acid or p-nitrophenoxyhexanoic acid as substrates41,42.
These reports are useful in obtaining polymers each having an aromatic ring in the side chain of PHA and having properties derived therefrom unlike general PHA whose side chain contains an alkyl group. Further, as the example of unusual-PHA having a cyclohexyl group, production of PHA from cyclohexylbutyric acid or cyclohexylvaleric acid has been reported43.
Moreover, as a new category, such studies are conducted that PHA having an appropriate functional group on a side chain is produced to try to produce a new function utilizing the functional group, not only the property change.
It is reported that a change of solubility in solvents has been found such that 3-hydroxyalkanoic acid having diol on the side chain terminal, synthesized by an oxidation reaction using potassium permanganate after producing PHA containing as a monomer unit 3-hydroxyalkenoic acid having an unsaturated bond in the terminal of the side chain using 10-undecenoic acid as a substrate, is rendered soluble in polar solvents such as methanol, acetone-water mixture (80/20, v/v) and dimethylsulfoxide, and insoluble in nonpolar solvents such as chloroform, tetrahydrofuran and acetone44.
It is reported that an improvement in speed of decomposition has been found for PHA containing 3-hydroxy-9-carboxynonanoic acid as a monomer unit, synthesized by an oxidization cleavage reaction using potassium permanganate after producing PHA containing as a monomer unit 3-hydroxy-10-undecenoic acid using 10-undecenoic acid as a substrate45.
However, the PHA in the above report is a copolymer of PHA (usual-PHA) composed of monomer units each having a carboxyl group at the end of its side chain and monomer units each having a straight-chain alkyl group on its side chain (usual PHA). As a result, the problems of low glass transition temperature etc. arise.
On the other hand, polymers each having an aromatic ring on its side chain are thermally stable and polymers having a carboxylphenyl unit are also expected to have high thermal stability, moreover, their carboxyl group is an active group applicable in various ways; accordingly, these polymers are very useful from the viewpoint of their application as functional materials.
[Technical Background of Toner]
So far, many methods have been known for electrophotography, and those methods are generally carried out in such a manner that an electric latent image is formed on an image-holding member (photosensitive member) by a variety of means using a photoconductive substance, the latent image is then developed with a toner to form a visible image, and the toner image is transferred onto a transfer material such as a paper as necessary, followed by fixing the toner image on the object transfer material by heat and/or pressure or the like to obtain a copy. For the method for visualizing the electric latent image, a cascade development method, a magnetic brush development method, a pressurizing development method and the like are known. Further, a method using a magnetic toner and a rotary development sleeve with a magnetic pole placed at the center thereof where the magnetic toner is caused to fly from the development sleeve onto the photoconductor by a magnetic field is also used.
Development systems for use in development of an electrostatic latent image include a two-component development system using a two-component type developer constituted by a toner and a carrier, and a one-component development system using a one-component type developer constituted only by a toner and using no carrier.
Here, the colored fine particle, so-called toner, has a binder resin and a coloring material as essential components, and in addition thereto, magnetic powders and the like as necessary.
<Binder Resin>
The bulk of a toner consists of a binder resin; therefore, the physical properties of the binder resin largely affect those of the toner. For example, the binder resin is required to have delicate hardness and heat fusion properties, while the toner, which is obtained by grinding and classifying the binder resin in which a colorant etc. is dispersed, is required to show a good flowability without producing fine powder even when subjected to mechanical impact by stirring in a developing equipment and without cohering and, at the time of its fixing, it is required to melt promptly at lower temperatures and, once it is melted, the melted toner is required to show cohesiveness. In other words, controlling the physical properties of the binder resin allows controlling the physical properties of the toner.
As a binder resin, traditionally, styrene-acrylic ester copolymer, polyester resin, epoxy resin, olefin resin, etc. have been used. And of these resins, polyester resin comes into extensive use as a resin for heat roll fixing toners, since it has advantages of good dispersion of toner additives, such as carbon black, wettability to transfer paper and superior fixing properties.
In recent years, people worldwide have become conscious of recycling of resources, reduction of wastes, improvement in safety of wastes, etc. from the viewpoint of environmental protection. These problems are not exception in the field of electrophotography. Specifically, with the spread of copiers and printers, the amount of toners fixed on paper, toner wastes and paper having been used for printing has increased year by year. Conventional toners, however, are all composed of stable artificial compounds, and hence hard to decompose; as a result, they can sometimes remain in every environment, such as in the soil and in water, for a long period of time. Further, one of the important considerations in recycling of resources is recycling and reusing plain paper; however, the conventional binder resins, typified by styrene resin, make hard the deinking by alkali hydrolysis, which is one of the problem in recycling plain paper. The safety of wastes is also an important consideration from the viewpoint of conservation of the global environment and effect on the human body.
<Application of Biodegradable Resin to Toner>
Also in the field of electrophotography, a method in which a biodegradable resin is used as a binder resin has been proposed as a method to realize a toner that can be discarded without environmental pollution.
For example, a Japanese Patent Application publication10 discloses an electrophotographic toner particularly for heated roll fixation characterized in that at least the binder resin contains a plant based wax and a biodegradable resin (e.g. polyester produced by microorganism, and natural polymer material of plant or animal origin), and the above described plant based wax is added in the above described binder in an amount of 5 to 50% by weight.
In addition, Japanese Patent Application publication11 discloses an electrophotographic toner containing a binder resin and a coloring agent, characterized in that the binder resin is composed of a biodegradable resin (e.g. aliphatic polyester resin), and the coloring agent is composed of non-water soluble pigments.
Further, U.S. Pat. No. 5,004,664 discloses a toner that includes, as a constituent, a biodegradable resin, in particular, polyhydroxybutyric acid, polyhydroxyvaleric acid, a copolymer or a blend thereof. With these prior arts, since the binder resins used are biodegradable, the toners can be certainly decomposed in the soil if they are disposed of by landfill; however, such resins are still problematic in essential functions as binder resins, specifically the durability as a toner is poor, and moreover, the charge characteristics of the toner are instable because of high hygroscopicity. For example, PHB is a hard and brittle material having a melting point of 180° C., a degree of crystallinity of 50 to 70%, a Young's modulus of elasticity of 3.5 GPa and an elongation percentage of 5%, inadequate for practical use as a toner binder.
There has been proposed toners including a polylactic acid-based aliphatic polyester, as a main ingredient, that are biodegradable, efficiently decomposed by alkali hydrolysis, and hence useful for recycling of paper. For example, there is proposed in Japanese Patent Application publication13 a method of producing a toner using lactic acid homopolymer, in which polylactic acid obtained by ring-opening polymerization process is shown as a representative example.
In the ring-opening polymerization process, an approach is adopted to subject lactic acid to dehydration reaction to form an oligomer, depolymerize the oligomer to lactide as a cyclodimer, and subject lactide to ring-opening polymerization. Since the method follows such a complicated procedure, the toner resin using the resultant polylactic acid becomes very costly.
Further, the ring-opening polymerization is a cationic ring-opening polymerization; as a result, it requires the steps of making the solvent used anhydrous; and removing ion species that serve as a polymerization inhibitor, which means low production efficiency. Furthermore, since the kind of monomer usable in the production of polyester is limited to cyclic ester, it is not easy to control the physical properties which the polyester is required to have as a resin for toners and it is also hard to copolymerize the monomer with other various monomers to control the balance of the degradability and the physical properties of the polyester obtained. In this respect, there have been demands for biodegradable polyesters which are inexpensive and whose physical properties are easy to control. If a toner is produced using polylactic acid, as a main ingredient, without any modification, problems of shelf stability and off-set resistance arise with the toner; therefore, such a toner has not come in practice yet.
There is disclosed in a Japanese Patent Application publication14 a toner for developing electrostatic charge images that is characterized by including: a polyester resin, which is obtained by subjecting a composition containing lactic acid and oxycarboxylic acid of three or more functional groups to dehydration polycondensation; and a colorant. In this toner, however, since the polyester resin is formed through the dehydration polycondensation reaction of the alcohol group of lactic acid and the carboxylic group of oxycarboxylic acid, the molecular weight of the resultant resin tends to be high, and therefore, its biodegradability probably tends to become low. Furthermore, problems of shelf stability and off-set resistance also arise with the toner composed of such a resin, like the toner disclosed in Japanese Patent Application Laid-Open No. H7-120975.
Further, there is disclosed in a Japanese Patent Application publication15 a toner for developing electrostatic charge images that is characterized by including: a urethane polyester resin, which is obtained by cross-linking polylactic acid with a polyvalent isocyanate of three or more functional groups; and a colorant. However, the polyester resin is also problematic in its of biodegradability, and problems of shelf stability and off-set resistance also arise with the toner composed of such a resin, like the toners described above.
Polycaprolactone, which is a typical homopolymer of hydroxycarboxylic acid, has a low melting point and a low glass transition point and, due to its melting point as low as 60° C., it alone is not suitably used as a binder resin, though it is excellent in compatibility with various resins. Polylactic acid has a high glass transition point (60° C.) and particularly that of crystallinity is a thermoplastic polymer having a high melting point (around 180° C.); however, it has not come in practice as a binder resin yet, as described above. Further, the conventional toner resins each composed of degradable polyester are generally poor in grindability, and they are difficult to use as a binder resin that accounts for 90% of a toner with particle diameter of about 10 μm. Thus, there has been a strong demand for improvement in the physical properties of the conventional resins from the viewpoint of their practical use as a binder resin for toners.
All of the toners for electrophotography described above use biodegradable resins as their binder resin and are recognized to produce the effect of contributing to the environmental conservation.
<Charge Controlling Agent>
For the method for imparting an electric charge to the toner, the electrifiability′ chargeability) of the binder resin itself may be used without using a charge controlling agent, but in this method, charge stability with time and humidity resistance are compromised, thus making it impossible to obtain high quality images. Therefore, the charge controlling agent is usually added for the purpose of maintaining and controlling the; charge of the toner.
Charge controlling agents well known in the art today include, for example, azo dye metal complexes, aromatic dicarboxylic acid-metal complexes and salicylic acid derivative-metal complexes as negative friction charging agents. In addition, as positive friction charging agents, nigrosine-based dyes, triphenylmethane-based dyes, various types of quaternary ammonium salts and organic tin compounds such as dibutyl tin oxide are known, but toners containing these substances as the charge controlling agent do not necessarily fully satisfy quality characteristics required for the toner such as the electrifiability and stability with time depending on their compositions.
For example, a toner containing an azo dye metal complex known as a negative charge controlling agent has an acceptable charge level, but may have reduced dispersibility depending on the type of binder resin to be combined because the azo dye metal complex is a low-molecular crystal. In this case, the negative charge controlling agent is not uniformly distributed in the binder resin, the charge level distribution of the obtained toner is significantly lacking in sharpness, and the obtained image has a low gray-level, resulting in a poor image formation capability. In addition, the azo dye metal complex has a unique color tone, and is thus presently used only for toners having limited colors around black, and if the azo dye metal complex is used as a color toner, its lack in clarity as a coloring agent required for obtaining an image having a high level of requirement for the color tone is a serious problem.
In addition, examples of almost colorless negative charge controlling agents include aromatic dicarboxylic-acid metal complexes, but they may be disadvantageous due to the fact that they are not perfectly colorless, and that they have low dispersibility peculiar to low-molecular-weight crystals.
On the other hand, nigrosine based dyes and triphenylmethane based dyes are presently used only for toners having limited colors around black because they are colored themselves, and may be poor in time stability of toners in continuous copying. In addition, conventional quaternary ammonium salts may have insufficient humidity resistance when formed into toners, and in this case, the stability with time may be so poor that high quality images are not provided as they are repeatedly used.
In addition, in recent years, attention has been given worldwide to reduction of wastes and improvement of safety of wastes in terms of environmental protection. This problem applies to the field of electrophotography as well. That is, as imaging apparatuses have been widely used, the amounts of wastes of printed papers, discarded toners and copying papers have increased year by year, and the safety of such wastes is important from a viewpoint of protection of global environment.
In the light of these problems, polymer charge controlling agents have been studied. Examples are the compounds disclosed in U.S. Pat. Nos. 4,480,021, 4,442,189 and 4,925,765, Japanese Patent Application publications20-22. Further, as polymer charge controlling agents that allow toners to exhibit negatively charged characteristics, copolymers of styrene and/or α-methylstyrene with alkyl(meth)acrylate ester or alkyl(meth)acrylate amide having a sulfonic acid group are often used23-27. These materials offer the advantage of being colorless; however, to obtain an intended amount of charge, a large amount of the materials needs to be added.
As described above, these compounds do not offer adequate performance as charge controlling agents, and problems of the amount of charge, charge build-up characteristics, stability over time and environment stability arise with them. Further, taking into consideration not only the functions of charge controlling agents, but also their effect on the human body as well as the environment, charge controlling agents are strongly wanted which can be produced using safer compounds by safer and moderate synthesis process and realize the reduction in amount of organic solvent used.
However, there has been known no report about the use of a biodegradable resin for a charge controlling agent, and there is still great room for improvement of charge controlling agent in view of the environmental conservation etc.
<Other Prior Art Documents>
In the invention of this application, the microorganisms described in elsewhere28,29 are used. The description of media in Reference 46 can also be quoted. The other techniques related to the invention of this application include, for example, techniques for obtaining carboxylic acid by cleaving carbon-carbon double bonds with an oxidizing agent30, 47-50 and a technique for synthesis of 5-(4-methylphenyl)valeric acid51.
In conventional plastic moldings, toner binders for toners and charge controlling agents used in electrophotography, resins have been used which will not be decomposed in the natural world and may cause various environmental problems when disposed of and the amount of such resins used tends to increase year by year. Under these conditions, there has been a strong demand that measures should be taken as soon as possible against waste disposal problems.
Thus, studies have been conducted on the use of biodegradable resins for these applications, as described above; however, the following problems have arisen with conventional biodegradable resins.
First, a polyester obtained by subjecting to a chemical reaction/treatment a polyester having the vinyl group reported so far can be given a variety of functions, but does not necessarily have satisfactory thermal characteristics because of the existence of a middle to long alkyl chain in the side chain. That is, the glass transition temperature and melting point of the polyester is low, resulting in significant limitations to the range of applications as moldings and films.
On the other hand, a polyester having an aromatic ring on the side chain generally has a high melting point and thus finds a wide range of applications as moldings and films as described previously. However, the polyhydroxyalkanoate type polyester having units each containing an aromatic ring substituted with a functional group capable of enduring a variety of applications includes only examples described above, and further more functional polyhydroxyalkanoate type polyesters have been desired.
This invention is made to solve the above described problems; accordingly, the object of this invention is to provide a polyhydroxyalkanoate-type polyester having a unit that includes an aromatic ring whose hydrogen is substituted with a carboxyl group, a functional group used for various applications, and a process for preparing the same.
Another object of this invention is to provide a resin composition that includes the above polyhydroxyalkanoate-type polyester and is capable of preventing the occurrence of various environmetal problems due to its disposal, moldings using the same, and a method of producing the moldings. Still another object of this invention is to provide moldings composed of biodegradable resins that are superior in various properties such as extrusion workability, mechanical properties and heat resistance, in particular, resin compositions having both biodegradability and heat resistance after molding.
As described above, the application of biotechnological approaches to the production of resin compositions and moldings makes it possible to produce novel resin compositions and moldings, which have been hard to realize by conventional synthetic-organic-chemistry approaches. Further, the application of biotechnological approaches often makes it possible to accomplish in one step a production process, which conventional synthetic-organic-chemistry approaches have done in more than one step. Thus, the application of biotechnological approaches is expected to produce various effects such as simplification of production processes, lowering of production costs and reduction of the time required for production processes. The application of biotechnological approaches also makes possible reduction in amount of organic solvents, acids, alkalis and surfactants used, establishment of moderate reaction conditions, and synthesis of resins from non-petroleum materials and low-purity materials. This allows the realization of an environmental load reduction and resource-recycle type of synthesis process.
The above described resin composition synthesis, which uses low-purity materials, will be described in further detail. In biotechnological synthesis process, generally substrate specificity of enzymes, as catalysts, is high; therefore, a desired reaction is allowed to proceed selectively even with low-purity materials. This means that resin wastes and recycling resin materials can also be expected as materials for resin compositions.
Another object of this invention is to provide a binder resin that includes the polyhydroxyalkanoate type of polyester, that is biodegradable and therefore capable of highly contributing to the conservation of the natural environment, that makes easy deinking in conventional deinking processes using an alkali and therefore promotes recycling of copying paper, and that satisfies various requirements for a toner, such as carrier spent, fog, charge stability, durability, storage stability, grindability and cost, a toner for developing electrostatic charge images that includes the above binder resin, and image forming method and apparatus using the toner.
In addition, the present invention provides a negatively charged charge controlling agent containing this polyhydroxyalkanoate type polyester, being more contributable to preservation of environments and the like, and having high performance (high charge level, quick start of charge, excellent stability with time, and high environmental stability) and improved dispersibility in the aspect of functionality, an electrostatic latent image developing toner containing the charge controlling agent, and an image formation method and an image forming apparatus using the electrostatic latent image developing toner.